Pigments have been conventionally used in a wide variety of applications, as they exhibit vivid color tones and high tinctorial strength. Among these pigments, those presenting practical importance in general are frequently of minute particles, and thus vivid color tones and high tinctorial strength are obtained by preventing the aggregation of the pigment particles and micronizing the particles. However, further micronization of the pigment results in an increase in the surface area, whereby particle aggregation is promoted, and thus many of such dispersions of pigment exhibit high viscosities. For this reason, when these pigment dispersions are prepared in an industrial scale, there occur problems such as that removal of the pigment dispersion from a dispersing machine becomes difficult, transportation through pipelines is not possible, or the pigment dispersion gelates during storage to become unusable.
Thus, it has been known hitherto that various dispersants are used to obtain pigment dispersions or colored photosensitive compositions having excellent fluidity, dispersibility and the like. These dispersants are roughly classified into polymeric dispersants and low molecular weight compound dispersants.
Examples of the polymeric dispersants include polyacrylic acid salts, sodium maleate olefin copolymers, terminal carboxyl group-containing polyesters (see, for example, Japanese Patent Application Publication (JP-B) No. 54-34009), polyesters having an acid group and/or a basic group, prepared from tetrakis(2-hydroxyalkyl)ethylenediamine as a starting material (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2-245231), macromonomers (oligomers having an ethylenic unsaturated group at the terminal), monomers having a hydroxyl group, copolymers including a carboxyl group-containing monomer and four species of monomers other than the carboxyl group-containing monomer (see, for example, JP-A No. 8-259876), and the like.
As for the low molecular weight compound dispersants, sorbitan fatty acid esters, polyoxyethylene alkylamines, alkyldiamines, alkanolamine derivatives and the like are known (see, for example, U.S. Pat. No. 3,536,510), and there are also exemplary dispersants having pigment nuclei introduced thereinto (see, for example, JP-B No. 5-72943, and JP-A No. 8-48890).
Meanwhile, a colored photosensitive composition containing a pigment is useful as a material for color filters used in solid state image pick-up elements, liquid crystal displays and the like, and in the case of producing a color filter using the colored photosensitive composition, a pigment dispersion process which is excellent in terms of quality, production stability or the like, is being widely employed.
Inter alia, when a color filter employing a pigment is used as a color filter for liquid crystal displays, it is required that the particle size of the colorant used (organic pigments, etc.) be finer (see, for example, JP-A No. 2000-321763). This is due to the fact that light scattering, birefringence and the like caused by the pigment result in the rotation of the polarization axis. If micronization of the pigment is insufficiently carried out, light scattering and absorption by the pigment bring forth a decrease in the light transmittance, thereby the display contrast being lowered, and the curing sensitivity at the time of patterning by exposure is decreased (see, for example, a color filter for 512-color display for 10.4-inch size TFT-LCD; Ueki, Ozeki, Fukunaga and Yamanaka, the 7th Color Optical Conference, 1990). For this reason, it is required for a colored photosensitive composition containing a dispersed pigment, that the pigment is dispersed in a micronized state.
As the pigment is micronized as described above, the surface area of the pigment is increased, and thus there is a tendency that the use of micronized pigment leads to an increase in the amount of dispersant to be added, which is needed to disperse the pigment in a curable composition. Furthermore, in a curable composition for the color filter application, the content of colorant (organic pigment) occupying among the solids is required to be higher for an improvement of color purity. However, if a dispersant or colorant is incorporated into a curable composition at a high concentration, the contents of photopolymerization initiator and photopolymerizable monomer occupying in the curable composition are relatively decreased. Thus, low energy curability is desired for an improvement in the yield rate through shortening of the exposure time for a curable composition, and on the other hand, there is a problem that it is difficult to obtain the curability in exposed parts.
Also for a curable composition for the use in color filters for solid state image pick-up element, low energy curing is desirable. With regard to a color filter for solid state image pick-up element, since film thickness reduction for colored patterns is in progress under the purpose of image quality improvement through high light harvesting property and high photo color separation property, the pigment concentration in the composition tends to increase along with this film thickness reduction.
Moreover, for a pigment-based color filter, color unevenness is likely to occur because the pigment consists of relatively coarse particles. Therefore, as the micronization of pigment is achieved to reduce this color unevenness, the content of pigment dispersant in the curable composition tends to increase. Accordingly, there is a problem concerning the difficulties in obtaining curability.
In order to cope with the problems such as color unevenness in a colored pattern formed, there has been suggested a technology of using an organic solvent-soluble dye as the colorant, in place of pigment (see, for example, JP-A No. 2003-029018). For such dye-based color filters, an increase in the concentration of dye is accompanied by significant problems such as a polymerization inhibitory effect originating from the dyes, or decreased stability over time as shown through dye precipitation.
As discussed above, with regard to a curable composition for the use in color filters, the contents of the photopolymerization initiator and the photopolymerizable monomer, which are necessary components for curing the curable composition, are limited, and the concentration of colorant has been increased, for both the applications in liquid crystal displays and solid state image pick-up elements. Thus, there have been problems of low sensitivity, unsatisfactory curing, insufficient adhesiveness to substrate, and the like.
In regard to these problems, a technology of improving the sensitivity by imparting polymerizability to a resin which has been introduced mainly to impart film forming property or developability, is being conventionally investigated (see, for example, JP-A Nos. 2000-321763 and 2003-029018, Non-Patent Documents “Color Filter the newest technology trend” pp. 85 to 87, published by Information Organization and “Advanced Technologies for LCD Color Filters” pp. 129 to 150, published by CMC Publishing Co., Ltd. (2006)).
However, even such resins as described above still cannot give satisfactory photosensitivity. Also, in fact, problems such as the generation of development residue in the unexposed parts, the image forming properties in the exposed parts, or a decrease in the color density (decoloration) due to the diffusion of fine pigment particles from the cured parts into the developer solution, still remain unsolved.
Furthermore, since the exposure sensitivity is insufficient, there also is a problem that curing occurs insufficiently in the deeper parts, such as the vicinity of the interface with a substrate, of a membrane prepared using a curable composition, thereby the adhesiveness to the substrate being poor, and the shape of the pattern becoming inversely tapered. Moreover, for the applications of color filters having a plurality of color patterns, there are also unresolved problems such as that when a pattern of a first color is formed, and then a coating solution for forming a pattern of a second color is applied, the pigment of the first color is diffused into the coating solution of the second color, or the color density is decreased (decolorized).